The present invention relates to a C-type column structure, and in particular to a C-type column structure that provides enhanced structural rigidity.
Many researchers are devoted to optimal design of rigidity for mechanical structures. Static and dynamic rigidity of the mechanical structures can be improved by analysis, enhancing dynamic precision during processing operations thereof. Conventionally, to obtain higher dynamic performance during design of a machine tool, structural configuration thereof is overly simplified. Thus, the analysis of the dynamic performance or rigidity of the machine tool is often inaccurate.
Referring to FIG. 1, a conventional machine tool (such as a CNC machine tool) comprises a column 1, a working table 20, and a spindle head 3. Two sliding rails 12 are disposed on the column 1. The spindle head 3 is slidably disposed on the sliding rails 12, moving upward and downward in Y-direction. The spindle head 3 can selectively hold a cutting tool. Sliding tables 21 and 22 are disposed on a base 2, respectively moving in Z-direction and X-direction. When a workpiece (not shown) is fixed on the working table 20, the machine tool can execute three dimensional processing by means of the cutting tool being fixed on the spindle head 3. Additionally, the conventional machine tool further comprises a balance weight (such as a metal piece, not shown) disposed in the interior of the column 1 and connected to the spindle head 3 by means of two chains 4. The balance weight can enhance rigidity or stability of the spindle head 3.
Nevertheless, when the workpiece is processed by the conventional machine tool, up and down processing movement of the spindle head 3 and forward, back, right, and left movements of the working table 20 cause vibration or resonance in the column 1. Errors by which the spindle head 3 processes the workpiece are thus generated. Also, the cutting tool or mold may be damaged, adversely affecting the performance of the machine tool.
Referring to FIG. 2, another column 5 is used in the machine tool to enhance the static and dynamic rigidity thereof. Specifically, the column 5 is substantially cuboid and hollow to reduce weight and material cost thereof. Further, the hollow interior of the column 5 is formed with a cellular structure. As shown in FIG. 2, a spindle head 6 can be slidably disposed on the column 5, moving up and down. Similarly, the column 5 can selectively hold a cutting tool.
Accordingly, to determine structural rigidity and probability of resonance of the column 5, ANSYS, engineering analytic software, can analyze and experiment with dynamic compliance and resonance frequency therefor. Specifically, the structural rigidity of the column 5 can be determined by the dynamic compliance analysis. Generally, the lower the dynamic compliance value, the better the anti-vibration capability of the column 5 and the higher the structural rigidity thereof. Moreover, higher resonance frequency values indicate that the column 5 is not easily resonated by external force. Based on analysis and experimentation with dynamic compliance and resonance frequency, resonance frequency values of the column 5 are shown in FIG. 3. When the spindle head 6 is on the top of the column 5 and a cutting force of 215 N along X-direction and a cutting force of 430 N along Z-direction are imitatively applied thereon, the dynamic compliance value of the column 5 is about 6.83×10−7 m/N. Generally, to assure sufficient rigidity of the column of the machine tool, the standard dynamic compliance value is 3×10−7 m/N. The dynamic compliance value (6.83×10−7 m/N) of the column 5, however, exceeds the standard dynamic compliance value (3×10−7 m/N). Namely, the column 5 will be easily deflected and deformed in Z-direction when subject to cutting forces.
As shown in FIG. 3, the resonance frequency value of the column 5 in the first mode is merely 55.489 Hz, easily causing resonance therein.
Hence, there is a need to provide an improved column structure that can remarkably enhance the structural rigidity thereof and reduce the weight thereof.